In contemporary fiber optic systems, optimization of coupling efficiency between the optical fiber and active or passive devices is a key metric in system comparisons, such as the pumps used in fiber amplification systems. In a popular technique for improving coupling efficiency, an end of the optical fiber is polished to provide a lens shape at the end face. Hyperbolic-shaped end faces are among the most highly desired shapes, since they tend to provide the highest coupling efficiency.
A popular technique for fiber polishing involves the use of a motor-controlled jig to position the end face of a fiber in contact with a rotating abrasive wheel. Once in contact, the end face of the optical fiber is polished by the wheel to form a lens.
The present invention is directed to a system and method for fiber polishing that overcome the limitations of conventional systems and methods. In particular, the present invention provides for continuous and contemporaneous determination of the extent of the polish during a polishing procedure. An optical signal is transmitted to a fiber tip, and any back-reflected signal is detected and monitored to determine the polish. In this manner, an automated polishing quality assurance is provided in real-time, during the polishing operation.
According to a first embodiment, the present invention is directed to a system for polishing a tip of a fiber optic. The system includes a fiber tip polishing unit for positioning a fiber optic tip relative to a polishing surface. A control system controls the positioning of the fiber optic tip. A polishing feedback unit includes an optical source and an optical sensing unit. During a polishing operation, the optical source provides an optical monitoring signal in the fiber optic, and the optical sensing unit senses a portion of the monitoring signal inwardly reflected (i.e., back reflected) from the tip.
The fiber tip polishing unit preferably positions the fiber optic tip relative to the polishing surface in a plurality of degrees of freedom. In the present implementation, the tip is held in a silicon chuck.
The fiber tip polishing unit may further include a bearing along a longitudinal axis of the fiber tip for providing the fiber tip at the polishing surface at a controlled force. The bearing may comprise an air bearing.
The fiber tip polishing unit may further include a translation positioner along a longitudinal axis of the fiber tip, the translation positioner being coupled to the control system for controlling longitudinal positioning of the fiber tip with respect to the polishing surface.
The fiber tip polishing unit may further include a rotation positioner along a longitudinal axis of the fiber tip, the rotation positioner being coupled to the control system for controlling rotational positioning of the fiber tip about the longitudinal axis with respect to the polishing surface.
The fiber tip polishing unit may further include a lateral positioner coupled to the control system for controlling lateral positioning of the fiber tip with respect to the polishing surface.
The polishing surface may comprise a rotating polishing pad, and the fiber tip polishing unit may further include a pad motor coupled to the control system for controlling rotation rate of the polishing pad. An optional tilt positioner may be coupled to the control system for controlling tilt angle of the polishing surface with respect to the fiber tip.
The polishing feedback unit may further include an optical coupler, for example a 3 dB coupler, for dividing the monitoring signal generated at the optical source, such that a portion of the monitoring signal is delivered to the fiber optic tip in a first direction of propagation, and such that a portion of the monitoring signal inwardly reflected from the tip is delivered to the optical sensing unit in a second direction of propagation. An optional termination unit, for example an index-matching gel, substantially eliminates back reflection of a remaining portion of the monitoring signal propagating in the first direction.
The optical sensing unit may further generate a feedback signal based on the sensed portion of the monitoring signal for controlling the positioning of the fiber optic tip.
The control system preferably controls positioning of the fiber optic tip by controlling spatial positioning or force and orientation of the tip with respect to, and contact force with, the polishing surface.
According to a second embodiment, the present invention is directed to a method for polishing a tip of a fiber optic. The position of a fiber optic tip relative to a polishing surface is controlled. During a polishing operation, an optical monitoring signal is provided in the fiber optic, and a portion of the monitoring signal inwardly reflected from the tip is sensed.
In this manner, an apparatus and method are provided for automated fiber polishing by which the quality of the polish is monitored during the polishing operation, and, in response, a control system performs a real-time adjustment of the polishing apparatus.